A huge crowd is expected to turn out at Auckland Airport this morning to greet the protester when he sets foot back in the country.

He has been in custody for five months since boarding a Japanese whaling ship in February before being given a two-year suspended sentence in a Tokyo court this week.

His wife, Sharyn, their two daughters, Danielle, 16, Alycia, 13, and their grandparents will be there to meet him.

"It will be so good to see him after just hearing his voice on the phone for five months," Mrs Bethune said. "I am not sure if he will be excited, tired or drunk – considering he has had no alcohol for so long."

His daughters could not wait to see their dad again. "They will give him big hugs and tell him not to misbehave in future," she said. They planned a quiet family dinner tonight to welcome him home.

Bethune, 45, pleaded guilty to four charges of illegally boarding the Shonan Maru 2 in February, but denied an assault charge.

Japanese prosecutors demanded two years' imprisonment, saying butyric acid, or rancid butter, that Bethune threw caused chemical burns to one whaler's face and hurt the eyes of several others.

Sobbing in the dock, Bethune said he thought his crew was going to die when the Sea Shepherd trimaran, Ady Gil, was sliced in two by a Japanese whaling ship.

"This broke my heart. I sold everything to develop the boat, it was my life," he said.

The Sea Shepherd group says banning Bethune from its Antarctic anti-whaling missions was just a legal strategy during his trial, and the New Zealand activist is welcome to join them on future trips.

His wife supported his actions and did not believe he should have been locked up. The ordeal had taken its toll, she said.

"I have heard he has lost weight, but if anyone could survive it, he could. He walked around his tiny cell 1200 times a day, clocking up 10 kilometres to keep fit. He always makes the best of any situation. We are very relieved he did not have to serve any more time."

Describing him as an adventurer, she expected him to stay at home for six months and write a book about his experiences.

Another New Zealand family trying to get a loved one home from behind bars overseas, the Cancian family of Lower Hutt, are not having the same success.

Danny Cancian, 43, is serving a five-year jail term in China for "excessive self-defence", after a man died as a result of a fight 20 months ago. His family had hoped Prime Minister John Key would discuss the possibility of a prisoner transfer during his visit to China, but that did not eventuate.